Thanks, Carl. That's was what I was hoping for.
There are two "Theories of Mercury" --- the old one,
that Mercury formed from inner disk materials, all
iron and refractories, and the new one, that Mercury
suffered a "Giant Impact' which added its iron to the
Mercurian core but blasted Mercury's crust off to be
lost.
Sometimes the Giant Impact Theory is interpreted
as a much-larger Mercury that lost much of its crust
to a series of Pretty Dam Big Impacts that contributed
no iron but blasted Mercury's crust off to be lost just
the same.
The old "All Iron And Refractories" theory seems, at
first glance, to be dead, but wait! there's still a heart
beat. The Crust is not The Planet. If Mercury has been
pasted through the ages by errant asteroids and comets
from Out-System that have been tossed down into high
eccentricity orbits, that crust of volatiles could be the
accretion of 4 billion years of Jupiter's trash toss-out.
There's a lot wrong with this idea. It's hard to deliver
material to Mercury without splashing it right off into
the grip of the Sun's powerful gravity, and it would
take a lot of material to pave a planet miles deep.
Perhaps the "anomalous" crust was delivered by the
Late Bombardment?
Sulfur, visible as yellow swirls, streaks and patches
surrounding the pits that burped it, got up and
screamed "Volatiles!" even before those scans were
released. It's just like Io, but a lot hotter. It can't
accumulate like it does on Io Still, if Mercury is
still boiling out sulfur after "billions and billions"
of years, it must have started with a LOT of volatiles.
Recent images of Mercury can be found at:
http://www.nasa.gov/mission_pages/messenger/multimedia/mercury_images_coll_archive_1.html
Maybe Mercury formed farther from the
Sun and migrated inwards...
It's a whole new solar system. Jumpin' Jupiter
wandering back and forth . Now, we have Migrating
Mercury. The problem is "migrated from where?"
Where do huge-iron-cored terrestrial planets with
scads of volatiles form? It's really hard to think of
any spot that provides vast amounts of both.
Sterling K. Webb
-------------------------------------------------------------------
----- Original Message -----
From: "Carl Agee" <a...@unm.edu>
To: <meteorite-list@meteoritecentral.com>
Sent: Sunday, June 19, 2011 11:16 AM
Subject: [meteorite-list] Mercury data
Of course it's still early days on understanding the Mercury data
coming back from Messenger, but I think there are a few simple things
that can be said about the two geochemical graphs that were part of
the press release. The major element graph of Al/Si versus Mg/Si
clearly shows that the measured Mercurian surface is similar to
basaltic and mantle rocks from the Earth. They plot along the Earth
array and look to be a bit more olivine-rich than mid-ocean ridge
basalts, but not as olivinerich as mantle peridotites, perhaps more
like Archean Earth komatiites. The measured Mercurian surface is NOT
delpleted in aluminum, like Martian basalts or Angrites. Also,
Messenger is clearly not measuring rocks like the lunar anorthositic
highlands. The major element that is still missing from this puzzle is
iron. The data do not say anything about the FeO content of the
Mercurian surface -- this is a pretty big deal, and until that is
known it will difficult to know exactly what we are looking at -- let
alone if there is a match for any known meteorite type.
The potassium/thorium plot shows that Mercury is a lot like the other
terrestrial planets in terms of volatile element content. It seems to
be closest to the K/Th of Mars which is quite surprising, since Mars
is thought to be the most volatile rich of the rocky planets. This
runs counter to the idea that the inner solar system is chemically
zoned with volatile elements concentrated out at Mars and lower in
towards the Sun. But who knows? Maybe Mercury formed farther from the
Sun and migrated inwards.
There was a brief mention of substantial amounts of sulfur, but no
data in the multimedia press release, so it would be interesting to
know what they mean by "substantial amounts". Also, why do they think
it is in the form of sulfide and not sulfate?
See how important these missions of planetary exploration are and how
fragmentary our understanding is?
Just my opinion....
Carl Agee
--
Carl B. Agee
Director and Curator, Institute of Meteoritics
Professor, Earth and Planetary Sciences
MSC03 2050
University of New Mexico
Albuquerque NM 87131-1126
Tel: (505) 750-7172
Fax: (505) 277-3577
Email: a...@unm.edu
http://epswww.unm.edu/iom/pers/agee.html
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